In time-of-flight (TOF) mass spectrometry, ions are mass-analyzed according to times of transit of ions, i.e., times required for ions to traverse a given length of passage. In TOF mass spectrometry, an assemblage of ions are accelerated with a given accelerating voltage from an ion source. These ions are emitted as pulses in a short time. Since a uniform accelerating energy is applied, ions of greater masses show smaller flight velocities. Ions of smaller masses exhibit greater flight velocities.
The assemblage of ions going out of the ion source with flight velocities according to mass are spatially dispersed according to flight velocity while traveling through a field-free drift region.
Ions having the minimummass of these ions first impinge on a detector Then, ions of greater masses sequentially reach the detector. The intensities of ions detected by the detector are recorded as a function of the elapsed time from the emission from the ion source. Thus, mass spectral information (hereinafter referred to simply as spectra) is obtained.
Where a mass analysis is performed using such a TOF mass spectrometer, ions should be ejected from the ion source at short intervals of time in order to make effective use of the ionized sample Consequently, more ions can be extracted within a limited time and mass-analyzed.
In TOF mass spectrometry, ions of smaller masses sequentially impinge on the detector and so if the ions are ejected at too short intervals of time, ions of smaller masses ejected later get ahead of previously ejected ions of greater masses and arrive at the detector. As a result, overlap of spectra takes place.